1. Field of the Invention
The invention relates to a microchip testing device for measuring the concentration of a component which is to be determined in a test liquid by means of absorption spectrum photometry using a microchip. Furthermore, the invention also relates to a microchip and microchip holder comprising this microchip testing device.
2. Description of Related Art
Recently an analysis process using a microchip called “μ-TAS” (μ-Total Analysis System) or “Lab-on-a-chip” has been attracting attention in which, using micromachinery production technology, chemical analyses and the like are performed in a more detailed manner than with conventional devices.
In this analysis system using a microchip (hereinafter also called a “microchip analysis system”), the effort is made to carry out all analysis treatment steps, such as mixing of the reagents, reactions, precipitations, extractions, determinations and the like, in an extremely small channel which is formed on a small substrate by micromachinery production techniques. Specifically, it is used, for example, for analyses of blood in the field of medicine, analyses of protein in extremely small amounts, analyses of molecules of living organisms, such as nucleic acids, and the like.
In particular, in the case of using a microchip analysis system for analyses of human blood, there are the following advantages:                1. For example, since only a small amount of blood is sufficient, the burden on the patient can be reduced.        2. Since only a small amount of reagent is sufficient, the analysis costs can be reduced.        3. Since the device is small, analyses can be easily carried out.        
It is being checked, whether using these advantages for a blood analysis device by the microchip analysis system, a specification can be stipulated in which the patient himself can analyze his blood, for example, at home or the like.
In a microchip analysis system, generally absorption spectrum photometry is used to measure the concentration of the portion of the substance which is to be determined in a test liquid (hereinafter, also called the “liquid to be tested”). Specifically, a microchip testing device is proposed in which the following actions were performed (see, for example, JP-A-2003-279471):                A mixture which contains an absorbance component which was obtained by adding a reagent to the liquid to be tested is allowed to flow into a channel which is formed, for example, in a microchip; the linear region of this channel is defined as the chamber for measuring absorbance;        the light, which was emitted by the light source and was transmitted by the chamber for measuring absorbance, is received by a light receiving part and the absorbance is determined; and        based on this absorbance, the concentration of the portion of the substance to be determined in the liquid to be tested was computed.        
In this microchip testing device, the amount of the liquid to be tested and the amount of reagent are extremely small. Furthermore, the absorbance measuring chamber must have at least a certain length according to the type of liquid to be tested. Therefore, for the chamber for measuring absorbance, it is necessary to have an extremely narrow shape and to make the surfaces of the light incidence part and light exit part very small (for example, roughly 0.5 mm2). For exact measurement of the absorbance, it is therefore necessary to prevent the light from emerging to the outside from the side of the absorbance measuring chamber by allowing light with high parallelism to be incident in the chamber for measuring absorbance, and thus, to prevent measurement errors from arising due to faulty radiation.
Here, the expression “faulty radiation” is defined as light which passes through a region outside the absorbance measuring chamber in the microchip and which is incident in the light receiving part.
The use of a laser device as the light source is ideal for supply of light to the chamber for measuring absorbance. However, since the laser light is monochromatic light and since, moreover, depending on the type of portion of the substance which is to be determined, the wavelength of the light which is necessary for measurement is different, it is necessary to provide a suitable laser device for each measurement; this is laborious and causes high testing costs. Therefore, use of a discharge lamp, such as a xenon lamp or the like, which emits light in a continuous wavelength range in combination with a wavelength selection means, such as a wavelength selection filter or the like, is being tested.
However, in a microchip testing device, the following is determined:                The intensity of the light (hereinafter called the “transmitted light intensity”) which emerges after passage through the absorbance measuring chamber into which the mixture has been introduced;        Based on this transmitted light intensity and the intensity of the light which is incident in the absorbance measuring chamber (hereinafter also called the “incident light intensity”) which was measured beforehand by, for example, pure water being introduced into the absorbance measuring chamber and measuring the intensity of the light which is transmitted and emerges from the absorbance measuring chamber into which this pure water was introduced, the concentration of the portion of the substance to be determined is computed according to the Lambert-Beer Law.        
In the case of using a discharge lamp, such as xenon lamp or the like, as the light source, there is the disadvantage that there is the danger that the value of the incident light intensity measured beforehand will differ greatly from the actual incident light intensity at the instant of measurement of the transmitted light intensity, since the discharge lamp has the property of changing the amount of radiant light over time, so that sufficient measurement accuracy cannot be obtained. This disadvantage is serious if there is a great time difference between the instant of measurement of the incident light intensity and the instant of measuring the transmitted light intensity.